﻿104 
  MR. 
  P. 
  R. 
  COWPER 
  REED 
  ON 
  THE 
  [Feb. 
  1 
  897, 
  

  

  common 
  structural 
  peculiarities 
  ; 
  (4) 
  the 
  similar 
  lithological 
  

   character 
  of 
  the 
  patches. 
  

  

  The 
  evidence 
  in 
  favour 
  of 
  the 
  brief 
  duration 
  of 
  the 
  fauna 
  consists 
  

   in 
  (1) 
  the 
  comparatively 
  slight 
  change 
  in 
  the 
  peculiar 
  facies 
  of 
  

   the 
  fauna, 
  despite 
  the 
  considerable 
  distance 
  apart 
  of 
  the 
  several 
  

   localities 
  ; 
  (2) 
  the 
  small 
  development 
  of 
  local 
  species 
  or 
  varieties 
  ; 
  

   (3) 
  the 
  little 
  impression 
  that 
  it 
  has 
  left 
  on 
  subsequent 
  faunas. 
  

  

  So 
  far, 
  therefore, 
  as 
  our 
  present 
  knowledge 
  goes, 
  we 
  may 
  look 
  

   upon 
  this 
  ' 
  Stage 
  P 
  ' 
  fauna 
  as 
  presenting 
  an 
  example 
  of 
  discon- 
  

   tinuous 
  distribution. 
  The 
  period 
  during 
  which 
  the 
  area 
  of 
  distri- 
  

   bution 
  was 
  continuous 
  lasted 
  only 
  during 
  the 
  time 
  necessary 
  for 
  

   the 
  migration, 
  and 
  it 
  was 
  therefore 
  so 
  transient 
  as 
  to 
  leave 
  scarcely 
  

   a 
  trace 
  behind 
  in 
  the 
  intervening 
  tracts 
  between 
  the 
  few 
  spots 
  

   where 
  the 
  fauna 
  was 
  able 
  to 
  take 
  root. 
  These 
  spots 
  now 
  alone 
  

   indicate 
  the 
  size 
  of 
  the 
  area 
  over 
  which 
  the 
  wave 
  of 
  migration 
  

   spread. 
  

  

  The 
  fact 
  that 
  the 
  limestone 
  in 
  each 
  of 
  these 
  ' 
  outposts 
  ' 
  or 
  

   ' 
  stations 
  ' 
  has 
  suffered 
  so 
  much 
  mechanical 
  disturbance 
  may, 
  

   perhaps, 
  be 
  in 
  the 
  main 
  attributable 
  to 
  its 
  reef-like 
  nature 
  and 
  

   mode 
  of 
  occurrence, 
  as 
  a 
  local 
  thickening 
  of 
  an 
  elsewhere 
  thin 
  band 
  

   of 
  rock. 
  But 
  I 
  do 
  not 
  wish 
  to 
  generalize, 
  or 
  to 
  imply 
  that 
  this 
  

   suggested 
  explanation 
  applies 
  to 
  those 
  examples 
  of 
  ' 
  reefs 
  ' 
  among 
  

   Devonian 
  and 
  Carboniferous 
  rocks 
  which 
  Mr. 
  Marr 
  has 
  quoted 
  

   (loc. 
  cit.). 
  Each 
  case 
  must 
  be 
  decided 
  independently 
  and 
  on 
  its 
  

   own 
  merits. 
  

  

  Summary 
  and 
  Conclusion. 
  

  

  As 
  the 
  result 
  of 
  the 
  above 
  detailed 
  inquiry 
  into 
  the 
  characters 
  of 
  

   the 
  fauna 
  of 
  the 
  Keisley 
  Limestone 
  and 
  the 
  relations 
  of 
  the 
  rock, 
  

   it 
  appears 
  to 
  me 
  that 
  the 
  following 
  facts 
  are 
  established 
  : 
  — 
  

  

  (1) 
  The 
  fauna 
  has 
  a 
  thoroughly 
  Ordovician 
  facies. 
  

  

  (2) 
  It 
  is 
  closely 
  comparable 
  with 
  that 
  from 
  the 
  Chair 
  of 
  

  

  Kildare 
  Limestone 
  and 
  that 
  of 
  the 
  Leptcena-Limestone 
  of 
  

   Dalecarlia, 
  and 
  less 
  closely 
  with 
  that 
  of 
  Stage 
  F 
  of 
  the 
  

   East 
  Baltic 
  provinces. 
  

  

  (3) 
  Its 
  palaeontological 
  features 
  point 
  to 
  its 
  stratigraphical 
  

  

  position 
  being 
  at 
  the 
  base 
  of 
  the 
  Upper 
  Bala. 
  

  

  (4) 
  It 
  must 
  be 
  regarded 
  as 
  the 
  locally-thickened 
  development 
  of 
  

  

  a 
  bed 
  which 
  is 
  elsewhere 
  in 
  Great 
  Britain 
  very 
  thin 
  or 
  

   entirely 
  absent, 
  or 
  represented 
  by 
  beds 
  of 
  entirely 
  different 
  

   lithological 
  characters 
  containing 
  a 
  different 
  fauna. 
  

  

  (5) 
  The 
  fauna 
  has 
  certain 
  unique 
  characters 
  which 
  mark 
  it 
  off 
  

  

  from 
  all 
  other 
  known 
  assemblages 
  of 
  fossils 
  in 
  Great 
  Britain. 
  

  

  Note. 
  — 
  Eecently 
  I 
  have 
  been 
  informed 
  by 
  Mr. 
  E. 
  Clark, 
  of 
  the 
  

   Geological 
  Survey 
  of 
  Ireland, 
  that 
  the 
  limestones 
  of 
  Toorma- 
  

   keady, 
  Co. 
  Mayo, 
  Courtown, 
  Co. 
  Wexford, 
  and 
  Caherconree, 
  Co. 
  

   Kerry, 
  are 
  lithologically 
  and 
  palaeontologically 
  (so 
  far 
  as 
  the 
  

   fossils 
  are 
  known) 
  identical 
  with 
  the 
  Kildare 
  Limestone. 
  At 
  present, 
  

  

  